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Managing nitrogen in corn this spring

By Daniel Kaiser and John Lamb, University of Minnesota Extension

ST. PAUL, Minn. (4/2/2012) —This unseasonably balmy weather has allowed for earlier field work to begin. How does this, coupled with an extremely dry fall, affect your nitrogen management program for corn?

If you applied nitrogen last fall
Field conditions were less than optimum for nitrogen application last fall. The dry soil conditions made it difficult for fall anhydrous ammonia application and the incorporation of urea. At this time, we would not expect a large amount of conversion of ammonium to nitrate within the soil if the fall applications were done according to nitrogen best management practices.

Soil sampling for soil nitrate-nitrogen at this time is unreliable and will likely not give an accurate picture of what is still contained within the soil.

If you made fall nitrogen applications and are concerned about how much nitrogen is left, our recommendation at this point is to wait until late May to early June, then use the supplemental nitrogen decision tool found at www.extension.umn.edu/go/1102 (pdf) to determine if a side-dress application is necessary.

If you did not apply nitrogen last fall

For sandy soils, you should not consider early application. The best practice for sandy soils is to apply nitrogen as part of the starter and a side-dress application.

For heavier textured soils, you may want to consider using a soil test for nitrate this spring to determine the suggested nitrogen application rate. Since we had a dry fall and winter, there is a good chance that there is a significant amount of soil nitrate left that the corn crop could use. This is particularly true if the previous crop was corn or small grains.

Soil conditions do appear to be ideal for application, but there is risk associated with application this early in the season. Nitrogen loss can occur with heavy rainfall events in April or May. The majority of the crop uptake occurs after the V5 growth stage, or when the plant is about a foot tall. Having most of the nitrogen in nitrate form when the plant is not actively growing does present some risk of loss.

The weather is warm now, but it is hard to tell what may occur a month or more later.

Any use of this article must include the byline or following credit line:
Daniel Kaiser and John Lamb are soil fertility specialists with University of Minnesota Extension.
Media Contact: Catherine Dehdashti, U of M Extension, (612) 625-0237, ced@umn.edu